The invention relates to a method for manufacturing an engine component comprising the steps of forming a component on a substrate by deposition of molten metal in subsequent layers to form said component into a desired shape, said component having an outer surface. The invention in particular relates to a manufacturing method suitable for the production of an engine structure in the form of a ring shaped structure particularly suitable as a gas turbine engine component.
A gas turbine includes a plurality of ring shaped metal structures which are assembled to form gas flow channels of the gas turbine. A gas turbine includes further engine components necessary for the function of the gas turbine. Examples of such components may be fuel injectors or vanes arranged to guide the flow through the gas flow channels of the gas turbine. In order to secure such an engine component to the ring shaped metal structure a protruding feature such as a stub, a boss a flange or a weld prep may be present on the surface of the ring shaped sheet metal structure in order to facilitate securing of the engine component to the ring shaped sheet metal structure.
The gas turbine may particularly be used as a jet engine. The term jet engine includes various types of engines, which admit air at relatively low velocity, heat it by combustion and shoot it out at a much higher velocity. Accommodated within the term jet engine are, for example, turbojet engines and turbo-fan engines. The invention will below be described for a turbo-fan engine, but may of course also be used for other engine types.
An aircraft engine of the turbofan type generally comprises a forward fan and booster compressor, a middle core engine, and an aft low pressure power turbine. The core engine comprises a high pressure compressor, a combustor and a high pressure turbine in a serial relationship. The high pressure compressor and high pressure turbine of the core engine are interconnected by a high pressure shaft. The high-pressure compressor, turbine and shaft essentially form a high pressure rotor. The high-pressure compressor is rotatably driven to compress air entering the core engine to a relatively high pressure. This high pressure air is then mixed with fuel in the combustor and ignited to form a high energy gas stream. The gas stream flows aft and passes through the high-pressure turbine, rotatably driving it and the high pressure shaft which, in turn, rotatably drives the high pressure compressor. The gas stream leaving the high pressure turbine is expanded through a second or low pressure turbine. The low pressure turbine rotatably drives the fan and booster compressor via a low pressure shaft, all of which form the low pressure rotor. The low pressure shaft extends through the high pressure rotor. In civil applications most of the thrust produced is generated by the fan while in military applications most of the thrust produced is generated by the low and high pressure turbines. Engine frames are used to support and carry the bearings, which in turn, rotatably support the rotors. Conventional turbo fan engines have a fan frame, a mid-frame and an aft turbine frame. These frames may be constructed by a gas turbine component comprising one or more ring shaped structures.
Different approaches of fabricating the ring shaped structures have been used in the past. Conventionally the ring shaped structure may be cast, where after the cast piece is machined to provide desired surface properties of the ring shaped structure. For instance, stubs forming a base for the attachment of an engine component may be formed in the machining process.
A novel approach to formation of the ring shaped structures may be performed by fabricating bosses, webs and stubs to a ring shaped sheet metal structure. Hence, the gas turbine component comprises a ring shaped sheet metal structure. The use of a sheet metal structure as a ring shaped element in the gas turbine facilitates production of thin gas turbine components.
This new manufacturing technology shows a great potential in reducing weight, shortening fabrication lead time and increasing flexibility in product development. Moreover, sheet material of a specific alloy has in general improved material properties compared to cast. Furthermore tighter tolerances of the thickness of the end product may be obtained with sheet metal in comparison to cast structures.
In the novel method of formation of a ring shaped structure including a step of fabricating a protruding feature such as a boss, a web and a stub to a ring shaped sheet metal structure the gas turbine component may furthermore include an engine component attached to the protruding feature. The protruding feature such as the stub, web or boss is deposited on said cylindrical sheet metal structure by use of a metal deposition technique.
The gas turbine component may furthermore include a plurality of webs deposited on said cylindrical sheet metal structure by use of a metal deposition technique. The plurality of webs may extend from said stub to take up load applied from said engine component via said stub and to reinforce said gas turbine component The inclusion of metal deposited webs ensures that a thin ring shaped sheet metal structure may be used, while allowing the webs to take up the load.
In metal deposition techniques a component or structure is formed by adding molten metal in a layer by layer fashion. The layers are fused together in the deposition process thus enabling the formation of a dense body. The layers are therefore not noticeable for practical purposes in the interior of the formed component. However, the layers may be discerned on the outer surface of the formed component as fine lines indicating the presence of different layers. On the surface of the layers, the edge portions of the layers will be slightly curved due to surface tension. The outer surface of the so-produced component must for many applications be subsequently machined in order to smooth out the plurality of curvatures at the edge portions of the layers.
It is desirable to provide a method defined in the introduction above, which method is more cost-efficient than prior art methods in achieving a component of equal or improved operational characteristics.
According to an aspect of the inventive method an engine structure is manufactured in a method including the steps of forming a component on a substrate by deposition of molten metal in subsequent layers to form said component into a desired shape, said component having an outer surface and re-melting at least part of said outer surface. In this way, an equal or improved surface smoothness of the component is achieved in relation to prior art methods, which in turn can reduce the risk of fatigue failure in operation. By the step of re-melting at least part of the surface, the shape of the part which is re-melted is transformed. Especially, the method comprises the step of forming the component on the substrate by deposition of a succession of layers on top of each other, wherein said at least part of said outer surface is defined by the ends of the layers in a layer extension direction.
Further, an improved microstructure can be achieved by said re-melting (smaller grains and thereby improved mechanical properties) due to a fast cooling.
By re-melting a lower rim of the component at an interface between the component and the substrate, the surface becomes smoother and stress concentration is reduced. It is particularly advantageous if the lower rim after the re-melting assumes a concave curvature, i.e a radius. The concave curvature allows for a relative large curvature radius at the transition between the substrate forming the engine structure and the deposited component.
Since stress concentration occurs at the transition between the engine structure and the component, the formation of a concave smooth surface at this area substantially reduces the risk for fatigue failure. Hence re-melting creates reshaping of the outer contour of the component from a set of convex outer rims, one for each layer, to a single concave area, preferably at a lower rim of the component, which lower rim adheres to an engine structure or which lower rim is intended to be mounted to an engine structure. This reshaping of the lower rim removes the necessity of further after-treatment steps such as milling.
According to an example, the method comprises the further step of depositing a plurality of the layers with different lengths in the layer extension direction so that said outer surface assumes a curvature. By depositing the layers in such a way, a base shape can be achieved before the re-melting step finally shapes the contour of the component.
Furthermore, by the step of re-melting, a surface roughness of the at least part of the outer surface which is heat treated is reduced. Due to the reduced surface roughness, the risk of fatigue failure is reduced. The component may be attached to an engine structure, but is preferably directly formed thereon by performing the deposition of molten metal in subsequent layers on said engine structure to form said component into a desired shape using said engine structure as a substrate. In this case the outer surface of said component includes a lower rim at which a transition between said component and said engine structure is located. The at least part of said outer surface which is heat treated is preferably constituted by the lower rim. The lower rim may preferably be constituted by outer rims of a number of layers being closest to the engine structure. For purpose of clarity it must be observed that the lower rim is not constituted by the inner parts of the lower layer which directly adheres to the engine structure, but of the outer rims of a set of layers being closest to the engine structure. By re-melting of the lower rim, it is ensured that the area at which stress concentration normally occurs has a reduced surface roughness whereby the risk for fatigue failure is substantially reduced.
According to a further example, the method step of re-melting at least part of said outer surface is performed without depositing any material.
According to a further example, said substrate is formed by a ring element for an engine structure and that the component forms part of a radial element extending from the ring element for guiding a gas flow through an engine in operation. Engine structures, in particular engine structures for gas turbine engines are subject to substantial load when used. The inventive method is therefore particularly advantageous for achieving an engine structure less sensitive to load when producing an engine structure in the form of a ring shaped gas turbine engine structure.
The inventive method may thus be used for production of an engine structure in the form of a ring shaped gas turbine component, where a component is metal deposited on the ring shaped sheet metal structure. The second component includes a lower rim at which a transition between said second component and said first component is located. The lower rim may thereafter be subjected to treatment with a heat source to reduce a surface roughness of said lower rim.